The invention is directed to a process for the production of 4-amino-6-tert.butyl-3-mercapto-1,2,4-triazin-5-one (I) ##STR2## in which in a first reaction step pivaloyl cyanide (II) ##STR3## is reacted with isobutylene in the presence of acetic acid and sulfuric acid and in a final reaction step the 4-amino-6-tert.butyl-3-mercapto-1,2,4-triazin-5-one (I) is formed by means of thiocarbohydrazide (III) ##STR4##
4-amino-6-tert.butyl-3-mercapto-1,2,4-triazin-5-one is an important intermediate product in the synthesis of the known herbicide 4-amino-6-tert.butyl-3-methylmercapto-1,2,4-triazin-5-one.
From German AS No. 2733180 (and related Klenk U.S. Pat. No. 4,175,188, the entire disclosure of which is hereby incorporated by reference and relied upon) there is already known a process for the production of 4-amino-6-tert.butyl-3-mercapto-1,2,4-triazin-5-one. In a first reaction step pivaloyl cyanide is reacted with isobutylene in the presence of acetic acid and 100% sulfuric acid and the trimethyl pyruvic acid tert.butylamide formed in this reaction is isolated. Subsequently the trimethyl pyruvic acid tert.butylamide is saponified by reacting with aqueous hydrochloric acid and the trimethyl pyruvic acid formed is isolated. In a final reaction step then the trimethyl pyruvic acid is subsequently condensed in aqueous-alcoholic solution with thiocarbohydrazide to form the 4-amino-6-tert.butyl-3-mercapto-1,2,4-triazin-5-one. In the industrial carrying out of the known process, however, the high accumulation of waste waters loaded with various types of inorganic and organic compounds is very disturbing. An economical working up of these waste waters is then hardly possible because of their complex composition. Besides the use of hydrochloric acid causes corrosion problems. Finally it is also not possible to at least partially recover the isobutylene employed.